function boom(){
	this.el = null;
	this.iTimer = null;
}
//创建
boom.prototype.create = function(){
	var 
		oBoxW  = $('box'),
		iNum   = Math.random() * parseInt(oBox.offsetWidth / 50),
		oPoint = createHtml('div');

	oPoint.className = 'point';
	oPoint.style.left = oBox.offsetLeft + iNum * 50 + 'px';
	document.body.appendChild(oPoint);

	this.el = oPoint;
	return this;
}
//运动
boom.prototype.move = function(){
	let iWinH = document.documentElement.clientHeight;
	var iTop = Math.random() * 20 + 10;
	this.iTimer = setInterval(function(){
		this.el.style.top = this.el.offsetTop + iTop + 'px';
		if (this.el.offsetTop > iWinH - this.el.offsetHeight) {
			this.el.remove();
		}
	}.bind(this),100)
}